This invention relates to a method for preparation of emulsifier for use in emulsion polymerization, by disproportionation reaction of rosin, polyunsaturated fatty acid, or a mixture thereof. The emulsifier can be suitably adapted to prepare polymers such as synthetic rubber, synthetic resin and the like by emulsion polymerization of monomers such as butadiene, styrene, chloroprene, acrylonitrile, etc.
Generally, rosin contains various kinds of resin acids, such as abietic acid, palustric acid, levopimaric acid, neoabietic acid. The molecular structures of such acids include conjugated diene and hence these resin acids have high chemical activities. Consequently, it has been known that using alkalie salt of the rosin which contains the resin acids, as emulsifier for production of synthetic rubber, for example, has a disadvantage, to wit, inhibition of normal polymerization. Thus, when using rosin as an emulsifier for emulsion polymerization, it is necessary to convert the resin acid having conjugated diene structure to its derivative having no conjugated diene structure.
There are many processes in the prior art related to disproportionation reaction of rosin in the presence of a catalyst. For examples, in U.S. Pat. No. 2,177,530, a method is disclosed for disproportionation of rosin using palladium-active carbon as a catalyst. U.S. Pat. No. 2,617,792 discloses a method using nickel as a catalyst. U.S. Pat. Nos. 2,407,248; 2,409,173; 2,494,550; 2,497,882; and 2,503,238 disclose methods using sulfur as a catalyst. U.S. Pat. Nos. 2,311,386 and 2,503,268 disclose methods using iodine as a catalyst. U.S. Pat. No. 2,395,278 discloses a method using sulfur dioxide as a catalyst. Among the foregoing catalysts, the most often used is palladium-active carbon catalyst. However, disadvantageously, it is known that the palladium-active carbon catalyst is effective only during the initial reactionstage of the disproportionation of rosin, to promote smooth reaction as a catalyst. As the reaction progresses, the activity of the catalyst is reduced and is ultimately lost. As an added disadvantage, it is impossible to reactivate the palladium-active carbon catalyst once it is spent.
Another disadvantage of palladium-active carbon catalyst is that when used in disproportionation reaction of either Tall Oil rosin or Tall Oil, due to the existence of traces of sulfur therein, the catalytic activity of palladium-active carbon is substantially reduced. To eliminate this defect, it is necessary to pretreat the Tall Oil rosin or Tall Oil to remove the sulfur trace, prior to disproportionation reaction. If there is no pretreatment to remove the sulfur trace, the amount of palladium-active carbon catalyst required would be so great as to make the process uneconomical. On the other hand, the pretreatment also entails added costs. Thus, use of palladium-active carbon as a catalyst is not advantageous from an industrial scale viewpoint. For wood rosin or gum rosin, such catalyst may serve some useful purpose.
Use of nickel as a catalyst also has disadvantages. During the disproportionation reaction of rosin, a part of the nickel catalyst reacts with the rosin to produce a salt of resin acid, and the resultant salt of resin acid dissolves itself in the rosin. Thus, after the reaction is completed, it is necessary to remove the nickel salt of resin acid dissolved in rosin, hence, making this process uneconomical.
Use of either selene or sulfur dioxide as a catalyst produces objectionable odors, although advantageously, there is obtained a light colored resultant disproportionated rosin. Thus, this method is not preferred.
It is known that using iodine as catalyst in disproportionation of rosin, disadvantageously, produces a lower softening point.
Polyunsaturated fatty acid, such as linolic acid, linolenic acid, eleostearic acid, has more than two double bonds in each molecular structure, as does rosin. It has been known that using polyunsaturated fatty acid as an emulsifier for emulsion polymerization may retard the polymerization reaction and inhibit normal progress of ordinary polymerization. When using fatty acid as emulsion polymerization emulsifier, such fatty acid containing polyunsaturated fatty acid and monounsaturated fatty acid, should be subjected to hydrogenation reaction so that the reaction is conducted on the polyunsaturated fatty acid with the utmost extent and not on the mono-unsaturated fatty acid. Suitable mild reaction conditions should be selected to acquire acceptable emulsifiers.